<div style="border:3px solid silver; width:300px;">
    <div id="DIV1" style="margin-bottom:50px; background-color:gold;">above</div>
    <div id="Float" style="float:left; background-color: green; width:100%;">Float</div>
    <div id="DIV2" style="margin-top:50px; background-color:gold;">below</div>
</div>